1. Field
The present disclosure relates to a water recovery method for beverage water or industrial water. More particularly, the present disclosure generally relates to a water recovery method for water from a natural system (for example, water obtained from a sea, river, lake, swamp, pond, and the like), wherein the water may be, for example, sea water, brackish water, river water, and the like, industrial drain water, various water drained from homes, and the like.
2. Description of the Related Art
A water recovery process (method) by an FO (forward osmosis) method is considered to lessen the energy consumption required for water recovery compared with a water recovery process by a RO (reverse osmosis) method. Accordingly, in recent times, developments on a water recovery process by an FO method have been actively made. Herein, the water recovery process by an FO method includes partitioning a low concentration solution (a solution subject to water recovery, for example sea water), and a high concentration solution having a higher osmotic pressure than the low concentration solution with a forward osmotic membrane, and inflowing water of the low concentration solution into the high concentration solution.
Specifically, in a water recovery process by an FO method, water of the low concentration solution flows into the high concentration solution using an FO membrane module. Herein, the FO membrane module includes a flow path for a low concentration solution where a low concentration solution is distributed, a flow path for a high concentration solution where a high concentration solution is distributed, and a forward osmotic membrane partitioning the flow path for a low concentration solution and the flow path for a high concentration solution. The high concentration solution may also be referred to be as a draw solution (DS). The water is recovered from the high concentration solution.
In a water recovery process by an FO method, because water moves spontaneously from a low concentration solution to a high concentration solution unlike a water recovery process by an RO method, it is not necessary to apply pressure to the low concentration solution.
Accordingly, the water recovery process by an FO method may lessen energy consumption for water recovery compared with the water recovery process by an RO method.
On the other hand, in a water recovery process by an FO method, FO membrane modules are coupled in series and thereby a large amount of low concentration solution may be treated. This process may be referred to be as a multiple water recovery process. In a conventional multiple water recovery process, a flow path for a low concentration solution and a flow path for a high concentration solution are respectively coupled in series. In addition, in the conventional multiple water recovery process, a low concentration solution is distributed in an in-series flow path for a low concentration solution including flow paths for a low concentration solution coupled in series, while high concentration solution is distributed in an in-series flow path for a high concentration solution including flow paths for a high concentration solution coupled in series.
However, in the conventional multiple water recovery process, as the number of steps from an inlet of an in-series flow path for a low concentration solution to an FO membrane module increases, an osmotic pressure difference between a low concentration solution and a high concentration solution in an FO membrane module decreases. This is because, as the number of steps from the inlet of the in-series flow path for a low concentration solution to an FO membrane module increases, the concentration of the low concentration solution in an FO membrane module becomes higher, and the concentration of the high concentration solution becomes lower. As the osmotic pressure difference between a low concentration solution and a high concentration solution decreases, an amount of water that flows from the low concentration solution to the high concentration solution decreases. Accordingly, in the conventional multiple water recovery process, water recovery efficiency decreases in an FO membrane module at a rear end, and furthermore recovery efficiency of the whole process also decreases.
A method of increasing a flow rate of a high concentration solution has been suggested to solve the above problem. However, this method requires high pump energy to distribute the massive amount of the high concentration solution. In addition, since water needs to be recovered from the massive amount of the high concentration solution, inconvenience of recovering water from the high concentration solution is increased. Thus, the method may not fundamentally solve the aforementioned problem.